/* Copyright 2002-2021 CS GROUP
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
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   */
  package org.orekit.propagation;
  
  import java.util.Collection;
  import java.util.List;
  
  import org.hipparchus.geometry.euclidean.threed.Rotation;
  import org.orekit.attitudes.AttitudeProvider;
  import org.orekit.attitudes.InertialProvider;
  import org.orekit.frames.Frame;
  import org.orekit.frames.Frames;
  import org.orekit.propagation.events.EventDetector;
  import org.orekit.propagation.sampling.OrekitFixedStepHandler;
  import org.orekit.propagation.sampling.OrekitStepHandler;
  import org.orekit.propagation.sampling.StepHandlerMultiplexer;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.PVCoordinatesProvider;
  
  /** This interface provides a way to propagate an orbit at any time.
   *
   * <p>This interface is the top-level abstraction for orbit propagation.
   * It only allows propagation to a predefined date.
   * It is implemented by analytical models which have no time limit,
   * by orbit readers based on external data files, by numerical integrators
   * using rich force models and by continuous models built after numerical
   * integration has been completed and dense output data as been
   * gathered.</p>
   * <p>Note that one single propagator cannot be called from multiple threads.
   * Its configuration can be changed as there is at least a {@link
   * #resetInitialState(SpacecraftState)} method, and even propagators that do
   * not support resetting state (like the {@link
   * org.orekit.propagation.analytical.tle.TLEPropagator TLEPropagator} do
   * cache some internal data during computation. However, as long as they
   * are configured with independent building blocks (mainly event handlers
   * and step handlers that may preserve some internal state), and as long
   * as they are called from one thread only, they <em>can</em> be used in
   * multi-threaded applications. Synchronizing several propagators to run in
   * parallel is also possible using {@link PropagatorsParallelizer}.</p>
   * @author Luc Maisonobe
   * @author V&eacute;ronique Pommier-Maurussane
   *
   */
  
  public interface Propagator extends PVCoordinatesProvider {
  
      /** Default mass. */
      double DEFAULT_MASS = 1000.0;
  
      /**
       * Get a default law using the given frames.
       *
       * @param frames the set of frames to use.
       * @return attitude law.
       */
      static AttitudeProvider getDefaultLaw(final Frames frames) {
          return new InertialProvider(Rotation.IDENTITY, frames.getEME2000());
      }
  
      /** Get the multiplexer holding all step handlers.
       * @return multiplexer holding all step handlers
       * @since 11.0
       */
      StepHandlerMultiplexer getMultiplexer();
  
      /** Remove all step handlers.
       * <p>This convenience method is equivalent to call {@code getMultiplexer().clear()}</p>
       * @see #getMultiplexer()
       * @see StepHandlerMultiplexer#clear()
       * @since 11.0
       */
      default void clearStepHandlers() {
          getMultiplexer().clear();
      }
  
      /** Set a single handler for fixed stepsizes.
       * <p>This convenience method is equivalent to call {@code getMultiplexer().clear()}
       * followed by {@code getMultiplexer().add(h, handler)}</p>
       * @param h fixed stepsize (s)
       * @param handler handler called at the end of each finalized step
       * @see #getMultiplexer()
       * @see StepHandlerMultiplexer#add(double, OrekitFixedStepHandler)
       * @since 11.0
       */
      default void setStepHandler(final double h, final OrekitFixedStepHandler handler) {
         getMultiplexer().clear();
         getMultiplexer().add(h, handler);
     }
 
     /** Set a single handler for variable stepsizes.
      * <p>This convenience method is equivalent to call {@code getMultiplexer().clear()}
      * followed by {@code getMultiplexer().add(handler)}</p>
      * @param handler handler called at the end of each finalized step
      * @see #getMultiplexer()
      * @see StepHandlerMultiplexer#add(OrekitStepHandler)
      * @since 11.0
      */
     default void setStepHandler(final OrekitStepHandler handler) {
         getMultiplexer().clear();
         getMultiplexer().add(handler);
     }
 
     /**
      * Set up an ephemeris generator that will monitor the propagation for building
      * an ephemeris from it once completed.
      *
      * <p>
      * This generator can be used when the user needs fast random access to the orbit
      * state at any time between the initial and target times. A typical example is the
      * implementation of search and iterative algorithms that may navigate forward and
      * backward inside the propagation range before finding their result even if the
      * propagator used is integration-based and only goes from one initial time to one
      * target time.
      * </p>
      * <p>
      * Beware that when used with integration-based propagators, the generator will
      * store <strong>all</strong> intermediate results. It is therefore memory intensive
      * for long integration-based ranges and high precision/short time steps. When
      * used with analytical propagators, the generator only stores start/stop time
      * and a reference to the analytical propagator itself to call it back as needed,
      * so it is less memory intensive.
      * </p>
      * <p>
      * The returned ephemeris generator will be initially empty, it will be filled
      * with propagation data when a subsequent call to either {@link #propagate(AbsoluteDate)
      * propagate(target)} or {@link #propagate(AbsoluteDate, AbsoluteDate)
      * propagate(start, target)} is called. The proper way to use this method is
      * therefore to do:
      * </p>
      * <pre>
      *   EphemerisGenerator generator = propagator.getEphemerisGenerator();
      *   propagator.propagate(target);
      *   BoundedPropagator ephemeris = generator.getGeneratedEphemeris();
      * </pre>
      * @return ephemeris generator
      */
     EphemerisGenerator getEphemerisGenerator();
 
     /** Get the propagator initial state.
      * @return initial state
      */
     SpacecraftState getInitialState();
 
     /** Reset the propagator initial state.
      * @param state new initial state to consider
      */
     void resetInitialState(SpacecraftState state);
 
     /** Add a set of user-specified state parameters to be computed along with the orbit propagation.
      * @param additionalStateProvider provider for additional state
      */
     void addAdditionalStateProvider(AdditionalStateProvider additionalStateProvider);
 
     /** Get an unmodifiable list of providers for additional state.
      * @return providers for the additional states
      */
     List<AdditionalStateProvider> getAdditionalStateProviders();
 
     /** Check if an additional state is managed.
      * <p>
      * Managed states are states for which the propagators know how to compute
      * its evolution. They correspond to additional states for which an
      * {@link AdditionalStateProvider additional state provider} has been registered
      * by calling the {@link #addAdditionalStateProvider(AdditionalStateProvider)
      * addAdditionalStateProvider} method. If the propagator is an {@link
      * org.orekit.propagation.integration.AbstractIntegratedPropagator integrator-based
      * propagator}, the states for which a set of {@link
      * org.orekit.propagation.integration.AdditionalEquations additional equations} has
      * been registered by calling the {@link
      * org.orekit.propagation.integration.AbstractIntegratedPropagator#addAdditionalEquations(
      * org.orekit.propagation.integration.AdditionalEquations) addAdditionalEquations}
      * method are also counted as managed additional states.
      * </p>
      * <p>
      * Additional states that are present in the {@link #getInitialState() initial state}
      * but have no evolution method registered are <em>not</em> considered as managed states.
      * These unmanaged additional states are not lost during propagation, though. Their
      * value are piecewise constant between state resets that may change them if some
      * event handler {@link
      * org.orekit.propagation.events.handlers.EventHandler#resetState(EventDetector,
      * SpacecraftState) resetState} method is called at an event occurrence and happens
      * to change the unmanaged additional state.
      * </p>
      * @param name name of the additional state
      * @return true if the additional state is managed
      */
     boolean isAdditionalStateManaged(String name);
 
     /** Get all the names of all managed states.
      * @return names of all managed states
      */
     String[] getManagedAdditionalStates();
 
     /** Add an event detector.
      * @param detector event detector to add
      * @see #clearEventsDetectors()
      * @see #getEventsDetectors()
      * @param <T> class type for the generic version
      */
     <T extends EventDetector> void addEventDetector(T detector);
 
     /** Get all the events detectors that have been added.
      * @return an unmodifiable collection of the added detectors
      * @see #addEventDetector(EventDetector)
      * @see #clearEventsDetectors()
      */
     Collection<EventDetector> getEventsDetectors();
 
     /** Remove all events detectors.
      * @see #addEventDetector(EventDetector)
      * @see #getEventsDetectors()
      */
     void clearEventsDetectors();
 
     /** Get attitude provider.
      * @return attitude provider
      */
     AttitudeProvider getAttitudeProvider();
 
     /** Set attitude provider.
      * @param attitudeProvider attitude provider
      */
     void setAttitudeProvider(AttitudeProvider attitudeProvider);
 
     /** Get the frame in which the orbit is propagated.
      * <p>
      * The propagation frame is the definition frame of the initial
      * state, so this method should be called after this state has
      * been set, otherwise it may return null.
      * </p>
      * @return frame in which the orbit is propagated
      * @see #resetInitialState(SpacecraftState)
      */
     Frame getFrame();
 
     /** Propagate towards a target date.
      * <p>Simple propagators use only the target date as the specification for
      * computing the propagated state. More feature rich propagators can consider
      * other information and provide different operating modes or G-stop
      * facilities to stop at pinpointed events occurrences. In these cases, the
      * target date is only a hint, not a mandatory objective.</p>
      * @param target target date towards which orbit state should be propagated
      * @return propagated state
      */
     SpacecraftState propagate(AbsoluteDate target);
 
     /** Propagate from a start date towards a target date.
      * <p>Those propagators use a start date and a target date to
      * compute the propagated state. For propagators using event detection mechanism,
      * if the provided start date is different from the initial state date, a first,
      * simple propagation is performed, without processing any event computation.
      * Then complete propagation is performed from start date to target date.</p>
      * @param start start date from which orbit state should be propagated
      * @param target target date to which orbit state should be propagated
      * @return propagated state
      */
     SpacecraftState propagate(AbsoluteDate start, AbsoluteDate target);
 
 }